====== TTP99-44 The three loop slope of the Dirac form factor and the 1S Lamb shift in hydrogen ======
 
 
   <hidden TTP99-44  The three loop slope of the Dirac form factor and the 1S Lamb shift in hydrogen > The last unknown contribution to hydrogen energy levels at order m alpha ^7,
 due to the slope of the Dirac form factor at three loops, is evaluated in a
 closed analytical form. The resulting shift of the hydrogen nS energy level
 is found to be 3.016/n^3 kHz. Using the QED calculations of the 1S Lamb
 shift, we extract a precise value of the proton charge radius
 r_p=0.883 \pm 0.014 fm.
 </hidden>
|**Kirill Melnikov and Timo van Ritbergen**  | 
|**  Phys. Rev. Lett.  84 1673-1676 2000  **  |
| {{preprints:1999:ttp99-44.pdf|PDF}} {{preprints:1999:ttp99-44.ps|PostScript}} [[http://arxiv.org/abs/hep-ph/9911277|arXiv]]   |
| |